The third ventricle from sheep brains will be analyzed by morphological methods to (1) assess the response of specialized ependyma, particularly tanycytes, to gonadal steroid hormone treatment, and (2) correlate structural changes with luteinizing hormone (LH) secretion from the anterior pituitary gland in the same animals. To determine the effect of estrogen (E2) and progesterone (P) on third ventricular cells and surfaces, and plasma LH, ovariectomized (OVX) ewes will be treated with E2, P and a combination of both. Blood samples will be drawn over the treatment period for radioimmunoassay (RIA) of plasma E2, P and LH. Hypothalami from these same animals will be examined with scanning and transmission electron microscopy and light microscopy (SEM, TEM, and LM). Particular attention will be paid to the infundibular recess where tanycytes predominate. To determine the effect of androgens on third ventricular cells and surfaces, and plasma LH, castrate rams will be treated with testosterone (T), with blood sampling and examination of the hypothalamic region of these animals as described above. To assess the temporal response of third ventricular ependyma in a physiologically normal situation, normally cycling ewes will be sacrificed at 3-day intervals over a 17-day estrous period. Blood samples for RIA of E2, P and LH will be obtained at sacrifice. Hypothalami of the same animals will be analyzed with SEM, TEM and LM. This interdisciplinary approach should lead to better understanding the structural basis for neuroendocrine regulatory mechanisms controlling the anterior pituitary gland. One potential health-related contribution may be improved methods of control of reproduction.